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플라즈마 이온질화 공정온도가 SCM440강의 내구성에 미치는 영향
정상옥(Sang-Ok Chong),박일초(Il-Cho Park),이천호(Cheon Ho Lee),김성종(Seong-Jong Kim) 대한용접·접합학회 2019 대한용접·접합학회지 Vol.37 No.5
In this study, plasma ion nitriding technology was applied to investigate the effect of plasma ion nitriding temperature and the surface roughness of SCM440 steel on the durability of SCM440 steel for gear material. The mechanical properties of the plasma ion nitrided specimens were examined using a comprehensive analysis of nitriding depth, phase change, microstructure and micro-Vickers hardness values. As a result, the durability of SCM440 steel was found to be more significantly affected by plasma ion nitriding temperature than surface roughness. As the plasma ion nitriding temperature increased, the composite phase of brittle γ"- Fe₄N + ε-Fe2-3N was converted into a single phase of γ"-Fe₄N, and the depth of the nitride layer increased, making it suitable for gear materials.
천연해수 용액에서 STS 304와 용융 알루미늄 도금된 STS 304의 캐비테이션-침식 환경 하에서의 전기화학적 특성
정상옥(Sang-Ok Chong),김성종(Seong-Jong Kim) 한국표면공학회 2016 한국표면공학회지 Vol.49 No.1
In this paper, the characteristics of a cavitation-erosion damage behavior on the STS 304 and hot-dip aluminized STS 304 under cavitation environment in sea water solution was investigated. The electrochemical experiments were carried out by potential measurement, anodic/cathodic polarization test, Tafel analysis, and also galvanostatic experiment in current density variables for the samples. The apparatus of cavitation-electrochemical experiment was manufactured in compliance with modified ASTM G-32 standard, with the conditions of sea water temperature of 25°C and the measurement, amplitude of 30 μm. The damage behavior was analyzed by an observation of surface mophologies and a measurement of damage depth by a scanning electron microscope(SEM) and a 3D microscope, respectively, after electrochemical test. After polarization experiment under cavitation environment, much higher damage depths for the hot-dip aluminized STS 304 were observed comparing to the untreated STS 304. In addition, higher corrosion current density in hotdip aluminized STS 304 presented than that of untreated STS 304 as a result of Tafel analysis.
알루미늄 용융 도금된 304 스테인리스강의 해수 내 전기화학적 부식 특성 평가
정상옥(Sang-Ok Chong),박일초(Il-Cho Park),한민수(Min-Su Han),김성종(Seong-Jong Kim) 한국표면공학회 2015 한국표면공학회지 Vol.48 No.6
Stainless steel has poor corrosion resistance in marine environment due to the breakdown of a passive film caused by chloride. It suffers electrochemical corrosion like pitting corrosion, crevice corrosion, and stress corrosion crack (SCC) in marine environment. In general, it indicates that the passive film of Al₂O₃ has better corrosion resistance than that of Cr₂O₃ in seawater. This paper investigated the damage behavior 304 stainless steel and hot-dip aluminized 304 stainless steel in seawater solution. Various electrochemical experiments were carried out including potential measurement, potentiodynaimic experiment, Tafel analysis and galvanostatic experiment. As a result of anodic polarization experiment, higher pitting damage depth was indicated at 304 stainless steel than hot-dip aluminized 304 stainless steel. In addition, relatively higher corrosion current density was shown at hot-dip aluminized stainless steel as a result of Tafel analysis.
해양 환경 하에서 431 스테인리스강의 하이브리드 실험을 통한 캐비테이션 손상 거동
정상옥(Sang-Ok Chong),김성종(Seong-Jong Kim) 한국표면공학회 2013 한국표면공학회지 Vol.46 No.6
The demand for stainless steel is continuously increasing with the development in offshore industry due to its excellent corrosion resistance characteristics. However, it suffers cavitation-erosion in application of high rotating fluid and the damage accelerates in combination with electrochemical corrosion because of Clion in sea water. This paper investigated the complex damage behavior for 431 stainless steel, that is one of martensite stainless steels, through the hybrid test in sea water. Various experiments were carried out, including potential measurement, anodic/cathodic polarization experiment and Tafel analysis. Surface morphology was observed and damage depth was analyzed by SEM and 3D microscope after each experiment, respectively. The results revealed that more active potential was observed under cavitation condition than static condition due to breakdown of passive film and activation of charge transfer, and that higher corrosion current density was obtained under cavitation condition due to synergistic effect of corrosion and erosion.
주조 스테인리스강의 해양환경 하에서 플라즈마 이온질화 공정온도에 따른 부식특성 연구
정상옥(Sang-Ok Chong),김성종(Seong-Jong Kim) 한국표면공학회 2017 한국표면공학회지 Vol.50 No.6
In order to improve corrosion resistance for cast stainless steel in seawater, the characteristics of corrosion resistance after plasma ion nitriding was investigated. Plasma ion nitriding process was conducted in a mixture of nitrogen of 25% and hydrogen of 75% at substrate temperature ranging from 350 to 500℃ for 10 hours using pulsed-DC glow discharge plasma with working pressure of 250 Pa in vacuum condition. Corrosion tests were carried out for as-received and plasma ion nitrided specimens. The corrosion characteristics were investigated by measurement of weight loss and observation of surface morphology. In anodic polarization experiment, relatively less damage depth and weight loss were presented at a nitrided temperature of 400℃, attributing to the formation of S-phase.
16Cr-10Ni-2Mo 스테인리스강의 정전류 실험에 의한 플라즈마 이온질화 온도 변수에 따른 부식 특성
정상옥(Sang-Ok Chong),김성종(Seong-Jong Kim) 한국표면공학회 2017 한국표면공학회지 Vol.50 No.2
The aim of this paper is to investigate the characteristics of electrochemical corrosion with the plasma ion nitriding temperature for 16Cr-10Ni-2Mo stainless steel. The corrosion behavior was analyzed by means of galvanostatic experiment in natural seawater that applied various current density with plasma ion nitriding temperature parameters. In result of galvanostatic experiment, relatively less surface damage morphology and the less damage depth was observed at a nitrided temperature of 450℃ that measured the thickest nitrided layer(S-phase). On the other hand, the most damage depth and unified corrosion behavior presented at a temperature of 500℃.
해양 환경 하에서 16.7Cr-10Ni-2Mo 스테인리스강의 표면 손상에 미치는 캐비테이션의 영향
정상옥 ( Sang Ok Chong ),한민수 ( Min Su Han ),김성종 ( Seong Jong Kim ) 한국부식방식학회(구 한국부식학회) 2015 Corrosion Science and Technology Vol.14 No.5
Stainless steel is generally known to have characteristics of excellent corrosion resistance and durability,but in a marine environment it can suffer from localized corrosion due to the breakdown of passivity film due to chloride ion in seawater. Furthermore, the damage behaviors are sped up under a cavitation environment because of complex damage from electrochemical corrosion and cavitation-erosion. In this study the characteristics of electrochemical corrosion and cavitation erosion behavior were evaluated on 16.7Cr-10Ni-2Mo stainless steel under a cavitation environment in natural seawater. The electrochemical experiments have been conducted at both static conditions and dynamic conditions inducing cavitation with different current density parameters. The surface morphology and damage behaviors were compared after the experiment.After the cavitation test with time variables morphological examinations on damaged specimens were analyzed by using a scanning electron microscope and a 3D microscope. the galvanostatic experiment gave a cleaner surface morphology presented with less damage depth at high current density regions. It is due to the effect of water cavitation peening under the cavitation condition. In the cavitation experiment, with amplitude of 30 ㎛ and seawater temperature of 25 ℃, weight loss and cavitation-erosion damage depth were dramatically increased after 5 hours inducing cavitation
스테인리스강과 양극산화된 알루미늄 합금의 전기화학적 부식특성에 미치는 해수온도의 영향
정상옥 ( Sang-ok Chong ),김성종 ( Seong-jong Kim ) 한국부식방식학회(구 한국부식학회) 2021 Corrosion Science and Technology Vol.20 No.2
The corrosion damage of materials in marine environment mainly occurs by Cl- ions due to the breakdown of passive films. Additionally, various characteristics in seawater such as salinity, temperature, immersion time, flow rate, and biological activity also affect corrosion characteristics. In this study, the corrosion characteristics of stainless steels (STS 304 and STS 316L) and anodized aluminum alloys (AA 3003 and AA 6063) were evaluated with seawater temperature parameters. A potentiodynamic polarization experiment was conducted in a potential range of -0.25 V to 2.0 V at open circuit potential (OCP). Corrosion current density and corrosion potential were obtained through the Tafel extrapolation method to analyze changes in corrosion rate due to temperature. Corrosion behavior was evaluated by measuring weight loss before/after the experiment and also observing surface morphology through a scanning electronic microscope (SEM) and 3D microscopy. Weight loss, maximum damage depth and pitting damage increased as seawater temperature increased, and furthermore, the tendency of higher corrosion current density with an increase of temperature attributed to an increase in corrosion rate. There was lower pitting damage and lower corrosion current density for anodized aluminum alloys than for stainless steels as the temperature increased.